Vision loss in a wide range of ischemic retinopathies such as retinopathy of prematurity and proliferative diabetic retinopathy is caused by aberrant neovascular growth and altered vascular barrier integrity. The overreaching goal of this proposal is to gain new insights into the pathogenesis of neovascular diseases by elucidating yet undefined vascular and inflammatory mechanisms driving sprouting angiogenesis and regressive remodeling of the retinal vasculature. a novel angiomodulatory system controlled byThe project focuses on the matricellular Cysteine-rich protein 61 referred to as CCN1. CCN1 is a central element of a pericellular network of bioactive extracellular matrix proteins acting through interaction with integrins to regulate diverse cellular functions. CCN1 is highly expressed by angiogenic endothelial cells (ECs) and macrophages at sites of active angiogenesis and inflammation. Research from the previous funding period has shown that CCN1-integrin signaling regulates vascular endothelial growth factor (VEGF) signaling, induces Notch-dependent intercellular communication and vessel specification and maintains barrier function. In cultured ECs, CCN1 is engaged in bidirectional molecular cross talks with the Hippo-Yes-Associated protein (YAP) pathway, a key checkpoint of tissue growth and homeostasis. We hypothesize that such functional interactions regulate the phenotypic plasticity of ECs during sprouting angiogenesis. Meanwhile, CCN1 is strongly expressed in macrophages involved in vasoobliteration and/or vessel involution so that CCN1 deficiency suppresses both macrophage-induced programmed fetal vessel regression and EC death. We hypothesize that CCN1-derived signals coordinate in cell type- and context-specific manner, the execution of multiple angiogenic and inflammatory programs that determine the angiogenic outcome under pathological conditions. Specific Aim 1 will (i) tease out the molecular bases of the CCN1-Hippo-YAP-regulatory axis in the endothelium, (ii) determine whether and how the CCN1-Hippo-YAP signaling pathway integrates other signaling cues (e.g., Notch, Wnt, VEGF) to produce a uniform angiogenic response, and (iii) define how this novel layer of extracellular signaling integration feeds on YAP function at the . Specific Aim 2 will determine (i) the role and significance of the CCN1-Hippo-YAP regulatory axis in retinal neovascularization and loss of barrier function using mouse models of oxygen-induced retinopathy and vascular permeability, and (ii) how CCN1 and YAP inter-regulation molecularly affects barrier gene expression level integrity. Specific Aim 3 will define the macrophage-derived CCN1 signals driving physiological remodeling of ocular vessels and the inflammatory response under ischemic conditions. It will identify macrophage-derived CCN1 signals critical for programmed pruning of retinal vessels and regressive remodeling of hylaoid vessels during development and determine whether priming macrophage-progenitors with CCN1 prevent retinal vascular damages induced by ischemia. This research will provide novel insights into the pathogenesis of ischemic retinopathies and identify effective targeted therapeutics curtailing both neovascular growth and inflammation.